core/collections

What problem does it solve? Managing entities in Redux state often leads to duplicated data, slow lookups, and mutation bugs. This Skill guides you to store entities in a normalized Collection shape with O(1) id lookup, stable ordering, and safe immutable updates. ## Core Features & Use Cases - Normalized Entity Storage: Create collections with createCollection and read them with getItem and getItems instead of storing plain arrays or Maps. - Immutable CRUD Helpers: Use addItem, updateItem, upsertItem, removeItem, and filterCollection so reducers never mutate .ids, .map, or .refsCount directly. - Reference Counting: Track shared entity ownership with addItemAndCountRef, increaseRefsCount, and decreaseRefsCount, which automatically removes items when their count reaches zero. - Use Case: When multiple features reference the same todo or user entity, store it once in a collection, count references per feature, and let the collection clean itself up when the last owner releases it. ## Quick Start Ask the AI to refactor a Redux slice that stores entities as an array into a Themis Collection with helper-based reducers and selectors.